The present invention relates to a mechanical pencil having a slidable actuator knob mounted on a tubular casing of the pencil, by which knob a writing lead is advanced when the knob is moved, and more particularly, to a mechanical pencil of the type described above which permits a lead-gripping chuck device to be opened to release its lead-gripping force when it is retracted, and to be closed to firmly hold the lead when same is advanced so that the writing lead can be projected from the tip of the mechanical pencil when the slidable knob is moved.
Generally known mechanical pencil of the type described has two types: one is a pencil in which a chuck device for holding the writing lead is retracted for the purpose of lead-projection, and the other is a pencil in which the chuck device is advanced for the same purpose, and the former type is advantageous in that the writing lead can be used up relatively economically to leave a relatively short remnant lead since it does not need additional space for forward movement of the chuck device, but on the other hand has a serious disadvantage that the writing lead is retracted, although very slightly, when a writing force is added to the lead together with the chuck device.
In view of the disadvantages of the prior art mechanical pencil of the type discribed above, a new mechanical pencil was suggested as disclosed in Japanese Utility Model Publication No. 62-37757, published Sept. 26, 1987 assigned to the present assignee, in which a resilient plate is generally engaged firmly with a tubular casing and disengaged easily with same by a pressure added sidewise by an actuator knob. However, the above described suggestion has another disadvantage that when a relatively high pressure of a writing force is added, the chuck actuator is retracted due to a resiliency of the resilient plate, with the result that the writing lead is retracted also.